1. Field of the Invention
The present invention relates to an improved process for manufacturing chloro-s-triazine triones which are sometimes referred to as chlorocyanuric acids or chloroisocyanuric acids. More specifically, this invention pertains to a method for preparing chloro-s-triazine triones, particularly trichloro-s-triazine trione, having enhanced crystal properties.
2. Description of the Prior Art
The preparation of chloro-s-triazine triones such as trichloro-s-triazine trione or dichloro-s-triazine trione is well known in the prior art.
One method for producing chloro-s-triazine trione is described in U.S. Pat. No. 2,969,360 issued Jan. 24, 1961. In this process, cyanuric acid (also known as s-triazine trione) is fed along with aqueous alkali (in molar ratio of about one mole of caustic per atom of chlorine to be attached) and chlorine to an aqueous reaction zone which is maintained at a pH in the vicinity of 3.5. The feed ingredients are added in essentially stoichiometric proportions. The crude chloro-s-triazine trione precipitates from the solution as a solid slurry. The slurry product is continually or periodically filtered to separate the crystalline products from the mother liquor whereupon the crystalline product is dried.
Prior art processes for producing chloro-s-triazine trione have been beset with numerous difficulties attributable to deficient particle size. For example, considerable manufacturing downtime and rate variances have been experienced in the manufacture of trichloro-s-triazine trione due to difficulties in water removal which result in a slushy feed to the dryer. When very wet or slushy product material reaches the dryer it becomes necessary to reduce the production rate or shut down the unit in order to avoid packaging wet trichloro-s-triazine trione. The primary cause for this problem is believed to be the very fine particle size produced in the process.
The patent literature reports other problems attributable to small particle size such as those relating to product separation (filtration), washing and drying as well as those relating to handling of the final dusty product. Small particle size is also said to decrease product stability.
It has been proposed heretofore in U.S. Pat. No. 3,120,522 issued Feb. 4, 1964, that chloro-s-triazine trione crystals having increased size can be produced by adding to the reaction mixture from which these crystals are formed, from 50 to 1,000 ppm of a chlorinated hydrocarbon containing 1 to 6 carbon atoms and having not more than one hydrogen atom in its molecule.
It has further been proposed in U.S. Pat. No. 3,427,314 issued Feb. 11, 1969, that increased particle size can be achieved by heating trichloro-s-triazine trione to from 130.degree. to 225.degree. C. with agitation and thereby causing the particles to agglomerate.
In addition, it has been proposed in U.S. Pat. No. 3,453,274 issued July 1, 1969, that crystal size of chloro-s-triazine triones may be increased by adding, as a surface active agent, an alkali metal alkyl sulfate or an alkali metal alkylarylsulfonate wherein the aryl portion is phenyl or naphthyl, to the reaction mixture while maintaining a pH between 1.0 and 4.5.
U.S. Pat. No. 3,941,784, which issued Mar. 2, 1976, teaches the crystal promotion of chloro-s-triazine trione by adding to the reaction mixture a small amount of polyoxyethylene, polyoxypropylene, or polyoxyethylene-polyoxypropylene copolymers.
The principal object of the present invention is to provide a chloro-s-triazine trione product having enhanced crystal properties and exhibiting outstanding stability when formulated with other chemicals in bleaching products. This object has been accomplished through use of certain crystal modifiers.